aboutsummaryrefslogtreecommitdiff
path: root/mm/kasan/shadow.c
blob: 80522d2c447b1977bbc9070a2d4dbe0a38ee6f06 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
// SPDX-License-Identifier: GPL-2.0
/*
 * This file contains KASAN runtime code that manages shadow memory for
 * generic and software tag-based KASAN modes.
 *
 * Copyright (c) 2014 Samsung Electronics Co., Ltd.
 * Author: Andrey Ryabinin <ryabinin.a.a@gmail.com>
 *
 * Some code borrowed from https://github.com/xairy/kasan-prototype by
 *        Andrey Konovalov <andreyknvl@gmail.com>
 */

#include <linux/init.h>
#include <linux/kasan.h>
#include <linux/kernel.h>
#include <linux/kfence.h>
#include <linux/kmemleak.h>
#include <linux/memory.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/vmalloc.h>

#include <asm/cacheflush.h>
#include <asm/tlbflush.h>

#include "kasan.h"

bool __kasan_check_read(const volatile void *p, unsigned int size)
{
	return check_memory_region((unsigned long)p, size, false, _RET_IP_);
}
EXPORT_SYMBOL(__kasan_check_read);

bool __kasan_check_write(const volatile void *p, unsigned int size)
{
	return check_memory_region((unsigned long)p, size, true, _RET_IP_);
}
EXPORT_SYMBOL(__kasan_check_write);

#undef memset
void *memset(void *addr, int c, size_t len)
{
	if (!check_memory_region((unsigned long)addr, len, true, _RET_IP_))
		return NULL;

	return __memset(addr, c, len);
}

#ifdef __HAVE_ARCH_MEMMOVE
#undef memmove
void *memmove(void *dest, const void *src, size_t len)
{
	if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
	    !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
		return NULL;

	return __memmove(dest, src, len);
}
#endif

#undef memcpy
void *memcpy(void *dest, const void *src, size_t len)
{
	if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
	    !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
		return NULL;

	return __memcpy(dest, src, len);
}

/*
 * Poisons the shadow memory for 'size' bytes starting from 'addr'.
 * Memory addresses should be aligned to KASAN_GRANULE_SIZE.
 */
void poison_range(const void *address, size_t size, u8 value)
{
	void *shadow_start, *shadow_end;

	/*
	 * Perform shadow offset calculation based on untagged address, as
	 * some of the callers (e.g. kasan_poison_object_data) pass tagged
	 * addresses to this function.
	 */
	address = reset_tag(address);

	/* Skip KFENCE memory if called explicitly outside of sl*b. */
	if (is_kfence_address(address))
		return;

	shadow_start = kasan_mem_to_shadow(address);
	shadow_end = kasan_mem_to_shadow(address + size);

	__memset(shadow_start, value, shadow_end - shadow_start);
}

void unpoison_range(const void *address, size_t size)
{
	u8 tag = get_tag(address);

	/*
	 * Perform shadow offset calculation based on untagged address, as
	 * some of the callers (e.g. kasan_unpoison_object_data) pass tagged
	 * addresses to this function.
	 */
	address = reset_tag(address);

	/*
	 * Skip KFENCE memory if called explicitly outside of sl*b. Also note
	 * that calls to ksize(), where size is not a multiple of machine-word
	 * size, would otherwise poison the invalid portion of the word.
	 */
	if (is_kfence_address(address))
		return;

	poison_range(address, size, tag);

	if (size & KASAN_GRANULE_MASK) {
		u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);

		if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
			*shadow = tag;
		else
			*shadow = size & KASAN_GRANULE_MASK;
	}
}

#ifdef CONFIG_MEMORY_HOTPLUG
static bool shadow_mapped(unsigned long addr)
{
	pgd_t *pgd = pgd_offset_k(addr);
	p4d_t *p4d;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;

	if (pgd_none(*pgd))
		return false;
	p4d = p4d_offset(pgd, addr);
	if (p4d_none(*p4d))
		return false;
	pud = pud_offset(p4d, addr);
	if (pud_none(*pud))
		return false;

	/*
	 * We can't use pud_large() or pud_huge(), the first one is
	 * arch-specific, the last one depends on HUGETLB_PAGE.  So let's abuse
	 * pud_bad(), if pud is bad then it's bad because it's huge.
	 */
	if (pud_bad(*pud))
		return true;
	pmd = pmd_offset(pud, addr);
	if (pmd_none(*pmd))
		return false;

	if (pmd_bad(*pmd))
		return true;
	pte = pte_offset_kernel(pmd, addr);
	return !pte_none(*pte);
}

static int __meminit kasan_mem_notifier(struct notifier_block *nb,
			unsigned long action, void *data)
{
	struct memory_notify *mem_data = data;
	unsigned long nr_shadow_pages, start_kaddr, shadow_start;
	unsigned long shadow_end, shadow_size;

	nr_shadow_pages = mem_data->nr_pages >> KASAN_SHADOW_SCALE_SHIFT;
	start_kaddr = (unsigned long)pfn_to_kaddr(mem_data->start_pfn);
	shadow_start = (unsigned long)kasan_mem_to_shadow((void *)start_kaddr);
	shadow_size = nr_shadow_pages << PAGE_SHIFT;
	shadow_end = shadow_start + shadow_size;

	if (WARN_ON(mem_data->nr_pages % KASAN_GRANULE_SIZE) ||
		WARN_ON(start_kaddr % KASAN_MEMORY_PER_SHADOW_PAGE))
		return NOTIFY_BAD;

	switch (action) {
	case MEM_GOING_ONLINE: {
		void *ret;

		/*
		 * If shadow is mapped already than it must have been mapped
		 * during the boot. This could happen if we onlining previously
		 * offlined memory.
		 */
		if (shadow_mapped(shadow_start))
			return NOTIFY_OK;

		ret = __vmalloc_node_range(shadow_size, PAGE_SIZE, shadow_start,
					shadow_end, GFP_KERNEL,
					PAGE_KERNEL, VM_NO_GUARD,
					pfn_to_nid(mem_data->start_pfn),
					__builtin_return_address(0));
		if (!ret)
			return NOTIFY_BAD;

		kmemleak_ignore(ret);
		return NOTIFY_OK;
	}
	case MEM_CANCEL_ONLINE:
	case MEM_OFFLINE: {
		struct vm_struct *vm;

		/*
		 * shadow_start was either mapped during boot by kasan_init()
		 * or during memory online by __vmalloc_node_range().
		 * In the latter case we can use vfree() to free shadow.
		 * Non-NULL result of the find_vm_area() will tell us if
		 * that was the second case.
		 *
		 * Currently it's not possible to free shadow mapped
		 * during boot by kasan_init(). It's because the code
		 * to do that hasn't been written yet. So we'll just
		 * leak the memory.
		 */
		vm = find_vm_area((void *)shadow_start);
		if (vm)
			vfree((void *)shadow_start);
	}
	}

	return NOTIFY_OK;
}

static int __init kasan_memhotplug_init(void)
{
	hotplug_memory_notifier(kasan_mem_notifier, 0);

	return 0;
}

core_initcall(kasan_memhotplug_init);
#endif

#ifdef CONFIG_KASAN_VMALLOC

static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
				      void *unused)
{
	unsigned long page;
	pte_t pte;

	if (likely(!pte_none(*ptep)))
		return 0;

	page = __get_free_page(GFP_KERNEL);
	if (!page)
		return -ENOMEM;

	memset((void *)page, KASAN_VMALLOC_INVALID, PAGE_SIZE);
	pte = pfn_pte(PFN_DOWN(__pa(page)), PAGE_KERNEL);

	spin_lock(&init_mm.page_table_lock);
	if (likely(pte_none(*ptep))) {
		set_pte_at(&init_mm, addr, ptep, pte);
		page = 0;
	}
	spin_unlock(&init_mm.page_table_lock);
	if (page)
		free_page(page);
	return 0;
}

int kasan_populate_vmalloc(unsigned long addr, unsigned long size)
{
	unsigned long shadow_start, shadow_end;
	int ret;

	if (!is_vmalloc_or_module_addr((void *)addr))
		return 0;

	shadow_start = (unsigned long)kasan_mem_to_shadow((void *)addr);
	shadow_start = ALIGN_DOWN(shadow_start, PAGE_SIZE);
	shadow_end = (unsigned long)kasan_mem_to_shadow((void *)addr + size);
	shadow_end = ALIGN(shadow_end, PAGE_SIZE);

	ret = apply_to_page_range(&init_mm, shadow_start,
				  shadow_end - shadow_start,
				  kasan_populate_vmalloc_pte, NULL);
	if (ret)
		return ret;

	flush_cache_vmap(shadow_start, shadow_end);

	/*
	 * We need to be careful about inter-cpu effects here. Consider:
	 *
	 *   CPU#0				  CPU#1
	 * WRITE_ONCE(p, vmalloc(100));		while (x = READ_ONCE(p)) ;
	 *					p[99] = 1;
	 *
	 * With compiler instrumentation, that ends up looking like this:
	 *
	 *   CPU#0				  CPU#1
	 * // vmalloc() allocates memory
	 * // let a = area->addr
	 * // we reach kasan_populate_vmalloc
	 * // and call unpoison_range:
	 * STORE shadow(a), unpoison_val
	 * ...
	 * STORE shadow(a+99), unpoison_val	x = LOAD p
	 * // rest of vmalloc process		<data dependency>
	 * STORE p, a				LOAD shadow(x+99)
	 *
	 * If there is no barrier between the end of unpoisioning the shadow
	 * and the store of the result to p, the stores could be committed
	 * in a different order by CPU#0, and CPU#1 could erroneously observe
	 * poison in the shadow.
	 *
	 * We need some sort of barrier between the stores.
	 *
	 * In the vmalloc() case, this is provided by a smp_wmb() in
	 * clear_vm_uninitialized_flag(). In the per-cpu allocator and in
	 * get_vm_area() and friends, the caller gets shadow allocated but
	 * doesn't have any pages mapped into the virtual address space that
	 * has been reserved. Mapping those pages in will involve taking and
	 * releasing a page-table lock, which will provide the barrier.
	 */

	return 0;
}

/*
 * Poison the shadow for a vmalloc region. Called as part of the
 * freeing process at the time the region is freed.
 */
void kasan_poison_vmalloc(const void *start, unsigned long size)
{
	if (!is_vmalloc_or_module_addr(start))
		return;

	size = round_up(size, KASAN_GRANULE_SIZE);
	poison_range(start, size, KASAN_VMALLOC_INVALID);
}

void kasan_unpoison_vmalloc(const void *start, unsigned long size)
{
	if (!is_vmalloc_or_module_addr(start))
		return;

	unpoison_range(start, size);
}

static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
					void *unused)
{
	unsigned long page;

	page = (unsigned long)__va(pte_pfn(*ptep) << PAGE_SHIFT);

	spin_lock(&init_mm.page_table_lock);

	if (likely(!pte_none(*ptep))) {
		pte_clear(&init_mm, addr, ptep);
		free_page(page);
	}
	spin_unlock(&init_mm.page_table_lock);

	return 0;
}

/*
 * Release the backing for the vmalloc region [start, end), which
 * lies within the free region [free_region_start, free_region_end).
 *
 * This can be run lazily, long after the region was freed. It runs
 * under vmap_area_lock, so it's not safe to interact with the vmalloc/vmap
 * infrastructure.
 *
 * How does this work?
 * -------------------
 *
 * We have a region that is page aligned, labelled as A.
 * That might not map onto the shadow in a way that is page-aligned:
 *
 *                    start                     end
 *                    v                         v
 * |????????|????????|AAAAAAAA|AA....AA|AAAAAAAA|????????| < vmalloc
 *  -------- -------- --------          -------- --------
 *      |        |       |                 |        |
 *      |        |       |         /-------/        |
 *      \-------\|/------/         |/---------------/
 *              |||                ||
 *             |??AAAAAA|AAAAAAAA|AA??????|                < shadow
 *                 (1)      (2)      (3)
 *
 * First we align the start upwards and the end downwards, so that the
 * shadow of the region aligns with shadow page boundaries. In the
 * example, this gives us the shadow page (2). This is the shadow entirely
 * covered by this allocation.
 *
 * Then we have the tricky bits. We want to know if we can free the
 * partially covered shadow pages - (1) and (3) in the example. For this,
 * we are given the start and end of the free region that contains this
 * allocation. Extending our previous example, we could have:
 *
 *  free_region_start                                    free_region_end
 *  |                 start                     end      |
 *  v                 v                         v        v
 * |FFFFFFFF|FFFFFFFF|AAAAAAAA|AA....AA|AAAAAAAA|FFFFFFFF| < vmalloc
 *  -------- -------- --------          -------- --------
 *      |        |       |                 |        |
 *      |        |       |         /-------/        |
 *      \-------\|/------/         |/---------------/
 *              |||                ||
 *             |FFAAAAAA|AAAAAAAA|AAF?????|                < shadow
 *                 (1)      (2)      (3)
 *
 * Once again, we align the start of the free region up, and the end of
 * the free region down so that the shadow is page aligned. So we can free
 * page (1) - we know no allocation currently uses anything in that page,
 * because all of it is in the vmalloc free region. But we cannot free
 * page (3), because we can't be sure that the rest of it is unused.
 *
 * We only consider pages that contain part of the original region for
 * freeing: we don't try to free other pages from the free region or we'd
 * end up trying to free huge chunks of virtual address space.
 *
 * Concurrency
 * -----------
 *
 * How do we know that we're not freeing a page that is simultaneously
 * being used for a fresh allocation in kasan_populate_vmalloc(_pte)?
 *
 * We _can_ have kasan_release_vmalloc and kasan_populate_vmalloc running
 * at the same time. While we run under free_vmap_area_lock, the population
 * code does not.
 *
 * free_vmap_area_lock instead operates to ensure that the larger range
 * [free_region_start, free_region_end) is safe: because __alloc_vmap_area and
 * the per-cpu region-finding algorithm both run under free_vmap_area_lock,
 * no space identified as free will become used while we are running. This
 * means that so long as we are careful with alignment and only free shadow
 * pages entirely covered by the free region, we will not run in to any
 * trouble - any simultaneous allocations will be for disjoint regions.
 */
void kasan_release_vmalloc(unsigned long start, unsigned long end,
			   unsigned long free_region_start,
			   unsigned long free_region_end)
{
	void *shadow_start, *shadow_end;
	unsigned long region_start, region_end;
	unsigned long size;

	region_start = ALIGN(start, KASAN_MEMORY_PER_SHADOW_PAGE);
	region_end = ALIGN_DOWN(end, KASAN_MEMORY_PER_SHADOW_PAGE);

	free_region_start = ALIGN(free_region_start, KASAN_MEMORY_PER_SHADOW_PAGE);

	if (start != region_start &&
	    free_region_start < region_start)
		region_start -= KASAN_MEMORY_PER_SHADOW_PAGE;

	free_region_end = ALIGN_DOWN(free_region_end, KASAN_MEMORY_PER_SHADOW_PAGE);

	if (end != region_end &&
	    free_region_end > region_end)
		region_end += KASAN_MEMORY_PER_SHADOW_PAGE;

	shadow_start = kasan_mem_to_shadow((void *)region_start);
	shadow_end = kasan_mem_to_shadow((void *)region_end);

	if (shadow_end > shadow_start) {
		size = shadow_end - shadow_start;
		apply_to_existing_page_range(&init_mm,
					     (unsigned long)shadow_start,
					     size, kasan_depopulate_vmalloc_pte,
					     NULL);
		flush_tlb_kernel_range((unsigned long)shadow_start,
				       (unsigned long)shadow_end);
	}
}

#else /* CONFIG_KASAN_VMALLOC */

int kasan_module_alloc(void *addr, size_t size)
{
	void *ret;
	size_t scaled_size;
	size_t shadow_size;
	unsigned long shadow_start;

	shadow_start = (unsigned long)kasan_mem_to_shadow(addr);
	scaled_size = (size + KASAN_GRANULE_SIZE - 1) >>
				KASAN_SHADOW_SCALE_SHIFT;
	shadow_size = round_up(scaled_size, PAGE_SIZE);

	if (WARN_ON(!PAGE_ALIGNED(shadow_start)))
		return -EINVAL;

	ret = __vmalloc_node_range(shadow_size, 1, shadow_start,
			shadow_start + shadow_size,
			GFP_KERNEL,
			PAGE_KERNEL, VM_NO_GUARD, NUMA_NO_NODE,
			__builtin_return_address(0));

	if (ret) {
		__memset(ret, KASAN_SHADOW_INIT, shadow_size);
		find_vm_area(addr)->flags |= VM_KASAN;
		kmemleak_ignore(ret);
		return 0;
	}

	return -ENOMEM;
}

void kasan_free_shadow(const struct vm_struct *vm)
{
	if (vm->flags & VM_KASAN)
		vfree(kasan_mem_to_shadow(vm->addr));
}

#endif